/*  
 *  Copyright 2006 Paul Jack.
 *
 *  This file is part of the Dex compiler suite. 
 *  
 *  Dex is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the
 *  Free Software Foundation; either version 2 of the License, or (at your
 *  option) any later version.
 *  
 *  Dex is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
 *  Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */
package dex.misc;

import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;


/**
 * Uses a linked list of hash maps to implement the Scope interface.
 *
 * @param <K>  the key type of the scope
 * @param <V>  the value type of the scope
 */
public class DefaultScope<K,V> implements Scope<K,V> {

	
	private LinkedList<Map<K,V>> layers;
	private List<Map<K,V>> readOnly;
	

	/**
	 * Constructs a new scope.
	 */
	public DefaultScope() {
		layers = new LinkedList<Map<K,V>>();
		readOnly = Collections.unmodifiableList(layers);
		add();
	}
	
	public void add() {
		layers.addFirst(new HashMap<K,V>());
	}
	
	
	public void remove() {
		if (layers.size() <= 1) {
			throw new IllegalStateException();
		}
		layers.removeFirst();
	}
	
	
	public List<Map<K,V>> layers() {
		return readOnly;
	}


	public Map<K,V> mostRecent() {
		return layers.getFirst();
	}

}
